High-pressure pump for cryogenic fluids



June 9, 1964 c. F. GOTTZMANN HIGH-PRESSURE PUMP Foa cRYoGENIc FLUIDSFiled oct. s, 1961 2 O l 3 3 m QW 4 .A l z l m M W Z E l. VTI m IY n 0Mn E j uw M f @a n l. A ISI :UIN R Y H B EV// u 2 n n m AIN 1l. I4.. WIT' 1| n ATTORNEY United States arent 3 136 136 HIGH-PRESSURE PUMP FCRCRYGGENIC FLUliDS Christian F. Gottzmann, Clarence, NY., assigner toInin Carbide Corporation, a corporation of New Filed Oct. 3, 1961, Ser.No. 143,521 24 Claims. (Cl. 62-55) This invention relates to apparatusfor storing and pumping a volatile liquid having a boiling pointtemperature at atmospheric pressure materially below 273 K., and moreparticularly to a reciprocating pump for pumping a liquelied gas havinga normal boiling point below 233 K., such as liquid oxygen, nitrogen,and the like, to an ultra-high pressure, for example, 10,000 p.s.i. Thepresent invention is a continuation-in-part of my cepending applicationsSerial No. 692,311, tiled October 25, 1957, now U.S. Patent 3,016,717,and Serial No. 12,130, filed March l, 1960, now abandoned.

Pumps heretofore proposed for pumping liquefied gases to high pressureshave involved difficulties due to the physical properties of the highlyvolatile liquids. For example, liquefied gases have greatercompressibility than water, and thus present greater heat of compressionproblems. come when the desired discharge pressure was below about 3,000p.s.i. On the other hand, the previously known pumps are eitherinefiicient or unworkable in the ultra-high pressure range above about5,000 p.s.i. This is because special problems, in addition to strengthconsiderations, arise which tend to decrease the efiiciency of theheretofore known pumps in this ultra-high pressure discharge range, andthese diiculties could eventually make the pumps inoperative. Theseunique problems are due to the increased pressure drop across theleakage path between the pump plunger and surrounding cylinder, greaterplunger forces and therefore higher plunger friction, and the largeramount of heat added to the liquefied gas during compression. The latterfact leads to vapor flashol from the liquid trapped in the clearancespace; that is, the portion of the pumping chamber not taken up orfilled by the plunger at the end of the discharge stroke, after thepressure in the pumping chamber has been released. Vapor flashoff inthis uniilled portion of the pumping chamber limits the amount of liquidthat can enter the pumping chamber during the suction stroke, and maycause the pump to become vapor bound and lose prime. The heretoforeproposed pumps have relatively large clearance spaces, which weretolerable with discharge pressure below about 3,000 p.s.i., but cannotbe tolerated when a pump must operate in the ultrahigh pressure range.

Another limitation of the heretofore known immersion pumps is therequirement of a relatively high pressure differential between thepumping chamber and the surrounding liquefied gas, to open the suctionvalve. This characteristic becomes critical in ultra-high pressureoperation, since the increased vapor liashoff results in a higherpressure in the pumping chamber at the end of the discharge stroke.Thus, to maintain the same pressure differential across the suctionvalve, it is necessary to supply the liqueiied gas in the surroundingcontainer at a relatively higher pressure. This requirement may increasethe operating costs of the system.

An additional problem not sufficiently overcome by the previouslyproposed systems for pumping volatile liquids to high pressures is thesubstantial transmission of heat from the atmosphere through the pumpmounting assembly into the container. This heat leak is partly due toconduction and also results from splashing of the liquefied gas againstthe pump mounting assembly, with result- However, these difficultieshave been largely overice ant wetting of the warm parts of thisassembly, thereby increasing the liquid evaporation rate. Because ofthis wetting, the heat leak problem is particularly acute when theimmersion pump-liquid container assembly is subject to considerablevibration and movement, or when the pump is mounted substantiallyhorizontally in the container. In the latter case, the pump mountingassembly is either directly immersed in the liquefied gas, or inrelatively close proximity thereto.

Still another disadvantage of the presently used immersion pumps is theslow plunger speed necessary to prevent excessive generation offrictional heat and to avoid the previously discussed excessive pressuredrop across the suction valve. A relatively low plunger speed requires alarger diameter pump cylinder or body to achieve a given pumping rate,and this in turn necessitates a massive pump body resulting in a highrate of heat transmission into the liquid bath inside and outside thepump and requiring a large opening in the container wall for pumpinstallation. The percentage of the liquid which leaks between theplunger and cylinder Wall also increases at slow plunger speeds.Finally, the forces imposed on the plunger and driving mechanism for agiven pumping rate are higher at slower speeds which adds to the expenseand massiveness of the entire assembly.

One object of the present invention is to provide a highly eicientimmersion pump for pressurizing liquefied gas to an ultra-high pressure.

Another object of the present invention is to provide areciprocating-type pump having a minimum clearance space.

A still further object is to provide a reciprocating-type immersion pumpwhich requires a relatively low pressure differential between thepumping chamber and the surrounding liquefied gas, to open the suctionvalve.

An additional object is to provide an immersion pumpliquid containerassembly whereby heat leak through the pump mounting assembly into thecontainer is minimized.

Another object is to provide a compact immersion pump which operates ata relatively high plunger speed but is characterized by low frictionalheat and low suction valve pressure drop thereby achieving low cost,high efficiency and operation dependability.

These and other objects and advantages of this assembly will be apparentfrom the following description and the accompanying drawings in which:

FIGURE 1 is a view of a vertical section through a pump according to thepreferred embodiment of the present invention;

FIGURE 2 is a plan view of the improved valve means;

FIGURE 3 is a section taken along the line 3--3 of FIGURE 2; and fFIGURE 4 is a fragmentary view of a partial section through the pumpbarrel and plunger, taken along line 4 4 of FIGURE 1.

The reciprocating pump of one embodiment of this invention comprises anelongated pump body having a pumping chamber at one end and an openingat the other end. An inlet or suction valve protrudes into the pumpingchamber and controls the inlet port which is situated near the end ofthe pumping chamber opposite the open end of the pump body. A dischargevalve is also provided to control a discharge outlet passage whichcommunicates with the pumping chamber for discharge of ultra-highpressure liquid therethrough. A reciprocating plunger extends throughthe pump body opening, the plunger having an inner end portioninterfitting with the inlet valve.' Thus, the clearance space in thepump of the present invention is appreciably reduced by having theplunger fill up at the end of the pump stroke a major part of theclearance space into which the suction valve projects into the pumpingchamber. In the preferred .3 embodiment of this invention, multiplesuction valves are used since they permit a smaller combined volume thana single valve and thus require less clearance space while alsoproviding a desired total opening area. Ball type inlet and dischargevalves are preferred in the immersion pump of the present inventionbecause they provide the most satisfactory and trouble-free pressureseal at ultrahigh pressures. Thus, it can be seen that the presentinvention provides a reciprocating pump having a substantially smallerclearance volume than the heretofore proposed pumps; that is, less thanabout 8 percent. One advantage of minimizing this space may beillustrated by the fact that for an immersion pump operating at 10,000p.s.i. discharge pressure and 15 F. subcooling, it is estimated thatthere will be a 3 percent loss in volumetric eiciency for each 1 percentincrease in clearance volume.

Another advantage of using multiple ball-type inlet or suction valves isthat a lower pressure drop is required to lift small multiple balls fromtheir seats during the suction stroke than is required to lift a largesingle ball. Pressure drop across the suction valve is critical in lowtemperature liquefied gas pumps because the liquid has a strong tendencyto ilash, thereby reducing the capacity of the pump and perhaps causingloss of prime. An inlet valve port with tageous in minimizing thispressure drop. With a single ported valve, a large port size requires alarge heavyweight ball valve; whereas, with multiple ports, the sameinlet port area may be obtained by using several valves,V

all of which are of uniform minimum weight. Furthermore, light-Weightmultiple balls are subjected to less impact during operation, and thusresult in a longer seat life. The required pressure differential may befurther reduced in the pump of the present invention by using hollowball-type inlet valves.

A still further novel feature of the provides an improved means forsealing present invention the annular space lbetween the pump body andthe concentrically positioned Walls of the opening in the sump chamberthrough which the pump is inserted, so as to minimize heat leak andliquid evaporation.

Referring now to the drawings, and specifically to FIG. 1, the pumpcomprises an elongated body 10 preferably in the form of a barrel havinga pumping chamber 12 in one end thereof, preferably the bottom, and anopening in the top or other end thereof. Mounted in the pumping chamber12 is an inlet valve assembly 14 which controls an inlet port 15 in thebottom of the body 10. A discharge valve 16 controls an outlet passage18 from the pumping chamber 12.

A reciprocating plunger 20 extends through the opening in the top of thebarrel 10 and has an inner pumping end portion 22 interitting with theinlet valve assembly 14 and substantially filling the clearance spacetherein. The opposite or upper end portion of the plunger 20 is providedwith Warm end packing means 24 spaced a substantial distance from thepump mounting ange 41 in an extension 24a of the pump body 10. Theextension 24a carrying packing gland absorbs suicient heat to avoidfreezing water vapor or condensible gases in the packing. A liowrestricting and plunger guide sleeve 25 is mounted in the pump body 10closely fitting the plunger with a sliding clearance. The upper endportion of the pump body 10 is surrounded by a vacuum jacket 26.

.Plunger 20 preferably ts the bore of the Working chamber fairly closelyto provide an easy sliding t. There should, however, be a smallclearance at working temperatures to permit a slight liquefied gas owalong the plunger. The flow restricting liner or guide sleeve 25 ispreferably disposed between the body portion 1i) and the plunger 20, thesleeve 25 having an internal cylindrical surface of a diameter similarto that of the pumping chamber 12. lt was found that a diametricalclearance between the plunger 20 and the guide sleeve 25 of 0.0020

' 20 and the sleeve 25 of less ythan a large cross-sectional area isadvanto 0.0035 inch at the low operating temperature permits freemovement of the plunger, and at the same time gives reasonably lowleakage rates. Although self-lubricating material, for example, a bondedgraphite or carbon is suitable for the sleeves 25 of pumps operatingwith discharge pressures in the range of about 3,000 p.s.i., suchmaterial has been found to be unsuitable for service in ultra-highpressure pumps because of the increased strength and ductilityrequirements. As a consequence, lubricant-containing metals arepreferred as the sleeve material for the pump of the present invention.Suitable materials include high graphite content sintered bronze, porousbronze impregnated with plastics such as polymerizedtetraiiuoroethylene, or chlorotrifluoroethylene, and porous bronzeimpregnated with a low pour point oil of a character compatible with theliquid pumped. These materials provide a low friction factor between theplunger about 0.35. A low thermal conductivity plastic spacer 25a ispositioned in the sleeve 25 to restrict the flow of heat generated byfriction due to plunger movement. The effect of the plastic spacer 25ais to break up the otherwise smooth temperature gradient between thewarm end of the pump and the pumping chamber 12, thereby reducing thetemperature of the walls in the pumping chamber. The spacer 25a ispreferably located just above the inner end of the plunger 2i? when ithas reached the end of the suction stroke. Suitable materials for theplastic spacer 25a include polytetrafluoroethylene, glass clothreinforced melamine resin, and cloth or ber reinforced phenolformaldehyde resin for processing inert gases such as nitrogen.Polytetraiiuoroethylene is also suitable for oxygen service. Also, inorder to minimize heat conduction from the cold or operating end of thepump, the body portion 10 is made as long and thin as is consistent withadequate strength. Preferably, the material employed also has a lowthermal conductivity to minimize longitudinal heat leak.

For venting the liqueiied gas llowing along the plunger V2t) from thepumping chamber 12, a passage means is provided preferably in the formof one or more vent passages or holes 54 in the upper part of the bodyportion 10. These holes S4 are preferably located as far towards thewarm end of the pump as practical in order to provide the longestpossible leakage path. This is because a long leakage path minimizes theamount of liquid leakage; and since liquid changes to gas with greatincrease in volume, the actual quantity or weight of leakage loss iskept very small. The vent holes 54 are closed by the plunger, but sincethere must be some small clearance for easy operation, a small amount ofthe gasied material pumped will escape from the pumping chamber 12through the vents 54.

The warm end of the sleeve 25 is retained by a mounting flange 53 at thelower end of the extension 24a. A packing box portion of the extension24a is lled with the packing means 24 which is retained by a glandfollower 24c and a packing nut 24d. The warm end of the plunger 20 issecured to a reciprocating mechanism by means not shown. A suitable typeof such warm end packing may be composed of asbestos and graphitecomposition rings which provide a sliding gas` seal. When the liquefiedgas to be pumped is liquid oxygen, a suitable type of packing may besimilar to that described in United States Patent No. 2,292,543 to I. F.Patterson.

The upper end portion of the pump body 10 is surrounded by a vacuumjacket 26 which reduces heat leakage into the cold region of sumpchamber 40 into which the pump body is inserted. Vacuum jacket 26preferably surrounds the pump body for about the length of annular heatexchanger 23.

An annular heat exchanger 23 surrounds the upper Y portion of the pumpbarrel 10 about 16 inches below the mounting iiange 41, and comprises anannular space surrounding the upper end of the pump body. TheV reducedwall thickness of the cylinder and the fins 27 shown in `FIG. 4 increasethe heat transfer. Alternatively to fins 27, the space may be providedwith helically wound strips whichrmay be corrugated, wrinkled or folded,to act as turbulence promoters,

The inlet valve assembly 14 is preferably multiple and as shown in FIGS.2 and 3 comprises an annular valve seat plate or disk 30 having aplurality of inlet ports 31 drilled therein, preferably eight as shownin an annular row. Each ball valve 32 is assembled over a correspondingport in the valve seat, and a valve retainer cage 34 is provided on thevalve seat 30 about the balls and secured in place on assembly. The cagefills the space between the balls and the pump barrel wall and providesa central opening for the plunger end. The valve assembly is slippedinto the lower end of the pump cylinder and secured by an externallythreaded annular or hollow nut 36 threaded into the end of the pump bodyto bear against the flanged lower end of the valve seat. This valvearrangement readily accommodates the requisite number of WSJ/16 inchdiameter balls for optimum simplicity and pressure drop.

The plunger 20 is preferably constructed of a precipitation-hardenablelow conductive stainless steel. If desired, conduction may be furtherreduced by making the plunger of thick-walled tubing with plugs weldedinto both ends substantially as shown. The ball valves 32 being arrangedaround the periphery of the valve body, the end 22 of the plunger 20 isstepped down so that it fills the space inside the circle of valves andannular ball cage 34. The clearance volume obtained by this constructionand cooperation between the plunger end and valve assembly is reduced toabout 31/2 For some plunger materials, for example Type 18-8 stainlesssteel, the plunger 20 is plated with about .005 inch thick chromiumplate to improve the surface hardness and wearing characteristics of thestainless steel and to reduce friction.

The diameter of the bottom 5'1/2 inches is reduced about .003 inch toavoid severe rubbing between this section of the plunger and the linerdue to any unavoidable curvature or bow in the plunger. Relievingtheeend of the plunger is highly beneficial in reducing the generationof friction in those parts of the pump in contact with suction liquid. Y

The pump is installed in a fore-chamber or sump 40 by bolting mountingflange 41 against sump flange 42. The sump consisted of inner container43 and outer container 44 with the space therebetween vacuum insulatedwith a high quality insulation such as alternate layer aluminum foil andglass fiber material as described` in copending patent applicationSerial No. 597,947 to L. C. Matsch led July 16, 1956, now U.S. PatentNo. 3,007,- 596, and Serial No. 824,690 to L. C. Matsch led July 2,1959, now U.S. Patent No. 3,009,601, and provided with liquid inlet andgas phase connections. Gas phase connection 4S is positioned just belowthe heat exchanger 23 and vacuum jacket 26. A lower extension of thesump with perforated head 46 forms a space for an adsorbent such asCalcium A Zeolite in acordance withV U.S. Patent 2,900,800. Sump liquidinlet connection 47 is located to pass through this space. The pump bodycan be withdrawn from the sump without breaking the vacuum in eithervacuum space or disturbing internal connections.

Liquid is drawn from the sump 40through the hollo-W nut 36, throughsuction ports 31 and around ball valves 32 into the pumping chamber 12.On the discharge stroke, liquid is expelled through discharge port 18around discharge valve 16 into the discharge tube 48. The fluid thenpasses through connection 50 into the annular heat ex' changer 23.

As the cold uid ows through heat exchanger 23 upward and around thissection of the pump, it intercepts and removes heat which otherwisewould reach the pumping chamber. Thus, the exchanger chills the upperregion of the pump below the mounting ange 41 and thereby reducessubstantially the temperature increment between the warm mounting flange41 and the pump chamber 12. In addition to removing atmospheric heatpassing down the pump by conduction, the discharge Huid helps removefriction heat generated in the upper section of the pump between theplunger 20 and the liner 25.

From the heat exchanger 23 the pump discharge fluid passes intodischarge line 52 and thence to usage. The line 64 shown opposite thedischarge line 52 extends through the packing housing flange 53, pumpange 41 and through the vacuum jacket gas tightly and into the gas phasespace of the sump, and provides a connection for a safety valve,bursting disk, and a pressure gauge.

The vent conduit 54 is located in the extension flange 53 and serves tovent the blowby or fluid leakage as previously described. The ventedmaterial may be blown to atmosphere or conducted to receiving means asdesired.

The vacuum jacket around the upper (warm) region of the pump preventsconvection between cold and warm levels along the outside of the pumpbody, and it also prevents sump (or tank) liquid from coming in contactwith the warm mounting flange. An effective insulator is very importantwhen pumping hydrogen or helium because it is imperative to minimizeheat transmission into the sump liquid.

Although the upward owing vent gas and discharge fluid greatly reducethe temperature of the pump inside the sump, it is unavoidable that theupper portions of the pump near the mounting flange will be relativelywarm due to solid conduction from the flanges and extension 24a. Sumpvapor coming in contact with such warm parts will circulate byconvection and transfer heat to the colder areas in the sump. Theaddition of a heavywalled heat exchanger jacket below the mountingilange tends to raise the temperature of the upper portion of the pumpdue to increased cross section area for longitudinal heat conductanceand to radial heat conductance from the relatively warm compresseddischarge fluid. Thus, the heat exchanger structure would normallyaggravate the convection problem. However, the vacuum jacket 26insulates the heat exchanger from the sump vapor and eliminates thisproblem. The outer wall of the jacket is relatively thin and does notconduct an appreciable quantity of heat.

Similarly, contacting the warm parts of the liquid splashes or otherwiserises above normal level.

In order to exclude effectively cold sump iiuids from the warm upperregions surrounding the pump, ythe vacuum jacket must make a moderatelygood seal against the sump wall at the lower (cold) end of the jacket.This must also be a sliding seal so that the pump can be easilyinstalled in and removed from the sump. One method of effecting thisseal is to provide the edge of the jacket below the bottom closure forthe vacuum 'space with a flared portion so that it makes a forced,sliding t into the sump. Uniform close clearance is thus maintainedbetween the jacket and the sump wall at this point. A

the vacuum jacket prevents sump liquid from preferred method of sealingis to provide a plastic O-ringY (e.g., Teflon or equivalent) around thelower end of the jacket as shown at 26a.

The space between the vacuum jacket 24 and the sump Wall 43 must be verynarrow throughout the length of the jacket in order to minimize oreliminate convection in this space. The diametral clearance between thetwo walls is preferably about .015 in.

Adequate benefits of the vacuum space are achieved simply by evacuatingthe space 26; no filler, reective shields or reective surfaces are used.A warm vacuum of about 1 to 10 microns is adequate. In practice, it isimportant that the vacuum jacket be removable from the sump withoutbreaking the vacuum in order to facilitate pump maintenance. Thispermits construction of the the pump in the event that'` ait-senso rv djacket as a factory-sealed unit with the pump assembly and with alljoints suiiiciently leak tight to obtain dependable, high-vacuumservice. An adsorbent or getter may be sealed in the lower end of thejacket to insure maintaining a good vacuum.

ln combination, the above-described features provide a more eicient pumpfor cryogenic service than heretofore possible. The unavoidablegeneration of friction heat by the moving plunger is minimized in thatportion of the pump which contacts suction liquid and is centeredprimarily in an intermediate section of the pump which v is in thermalcontact with the discharge iluid. The discharge liquid, together withthe fluid unavoidably leaking by the plunger, absorbs and removes themajor portion of the friction heat and also reduces heat inleak bychilling the intermediate section. A vacuum jacket removable with thepump assembly prevents suction iluids from contacting the warm end partsand the intermediate section of the pump Where friction heat is beingremoved. Spacing the packing well beyond the chilled section on ahousing extension and venting the plunger leakage aford warm temperatureand low pressure at the packing, thereby reducing friction.

What is claimed is:

1. A reciprocating pump for liquefiedV gases having a boiling pointbelow 273 K., said pump comprising an elongated pump body having apumping chamber therein adjacent one end and an opening at the otherend; an inlet valve controlled port near the end of said pumping chamberopposite said opening; an inlet valve assembly positioned to controliiow through said port having an inlet valve protruding into saidpumping chamber such that a space is provided at the lower end of saidpumping chamber not occupied by the valve assembly; a reciprocatingplunger extending through said opening in the pump body having an innerpumping end portion operable in said pumping chamber and constructed andarranged to interlit with said inlet valve to substantially lill saidspace when at the end of a discharge stroke; a discharge valve anddischarge valve-controlled port near the end of said pumping chamber;Warm end packing means for the portion of the plunger extending throughsaid opening, said packing means being spaced at a substantial Ydistance from said pumping chamber; and a ow restrictive sleeve in saidpump body, closely fitting said plunger. 2. A reciprocating pumpaccording to claim 1 wherein insulating means surrounds a portion ofsaid pump body adjacent the warm end thereo 3. A reciprocating pumpaccording to claim l wherein a heat exchanger passage surrounds aportion of said pump body adjacent the Warm end thereof and isinterposed in said discharge valve controlled outlet passage such thatthe liquid expelledthrough said discharge valvecontrolled port passesthrough said heat exchanger.

4.7A reciprocating pump for liquefied gases according to claim 1 inwhich said flow restricting sleeve comprises portions made of alubricant-containing metal and at least one low thermal conductivityplastic spacer interposed between said portions so as to minimize theliow of frictional heat along the sleeve.

5. A reciprocating pump for liquefied gases according to claim 1 inwhich said flow restricting sleeve comprises portions made of alubricant-containing metal which affords a friction factor between saidp-lunger and the sleeve of less than about 0.35; said plunger and sleevebeing sized so as to provide a diametrical clearance of about 0.0020 to0.0035 inch at the low operating temperature.

6. A reciprocating pump according to claim 1 Ywherein said plunger isVhollow, constructed of low-conductive material, and sealed at both ends.

7. A reciprocating Apump according to claim 6 wherein said pump body hasa bore receiving said hollow low-conductive plunger with a clearanceforming lan extended blowby passage in heat exchange with said plungerand t3 a plunger covered vent is provided in the pump body wall adjacentthe warm end thereof. Y

8. A reciprocating pump vaccording to claim 2 wherein said insulatingmeans comprises a vacuum jacket constructed to maintain a low positivepressure below atmospheric about 10 microns of mercury absolute.

9. A reciprocating pump according to claim 8 wherein said pump body isinstalled in a sump and the diametrical clearance between the vacuumjacket and the inner wall of said sump is sufficiently close in order toprovide a sliding seal between said vacuum jacket and said sump, andincluding sealing means to eifect such seal.

10. A reciprocating pump according to claim 3 wherein said heatexchanger comprises kan outer wall, an inner wall having radiallyoutward projecting heat transfer fins, and a fluid space therebetweenconnecting to said discharge valve controlled outlet passage.

11. A reciprocating pump according to claim 3 wheren said heat exchangercomprises an outer wall, an inner wall having outward projectinghelically wound heat transfer strips, and a fluid space therebetweenconnecting to said discharge valve controlled outlet passage.

12. A reciprocating pump for liquefied gases having 'a boiling pointbelow 273 K., said pump comprising an elongated pump body insertable ina sump chamber adapted to receive said pump body, said pump body havinga pumping chamber therein adjacent one end and an opening at the otherend; an inlet valve controlled port near the end of said pumping chamberopposite said opening; an inlet valve assembly positioned to controltlow through said port having an inlet valve protruding into saidpumping chamber such that a space is provided at the lower end of saidpumping chamber not occupied by the valve assembly; a reciprocatingplunger extending through said opening in the pump body having an innerpumping end portion operable in said pumping chamber and constructed andarranged to interi'it with said inlet valve to substantially till saidspace when at the end of a discharge stroke; a discharge valve anddischarge valve-controlled port near the end of said pumping chamber;warm end packing means for the portion of the plunger extending throughsaid opening, said packing means being spaced at a substantial distancefrom said pumping chamber; and a flow restrictive sleeve. in saidpump-body closely iitting said plunger; a heat exchanger .surrounding a.portion of said pump body adjacent the Warm end thereof and a vacuumjacket surrounding said heat exchanger, said heat exchanger comprisinginner and outer walls and a fluid space therebetween connecting to saiddischarge valve controlled outlet passage; and a sump chamber comprisinginner and outer walls and having an open end for receiving said pumpbody and said vacuum jacket such that the insertion of said pump bodyiluid tightly seals said open end and such that said vacuum jacket isremovable from said sump without breaking the vacuum therein, theinterior of said sump chamber communicating with a fluid inlet conduitand the pump inlet valve-controlled port.

13. A reciprocating pump for liqueed gases having a boiling point below273 K., said pump comprising an elongated pump body having a pumpingchamber therein adjacent one end and an opening at the other end;multiple inlet valves in said pumping chamber and surrounding a centralspace therein, and an inlet valve-controlled port near the endV of saidpumping chamber opposite said opening; a discharge valve and a dischargevalve-controlled outlet passage from the pumping chamber; areciprocating plunger extending through said opening in the pump bodyhaving an inner pumping end portion operable in said pumping chamber andhaving a reduced end of a size and shape for'substantially filling saidcentral space at the end of the discharge stroke; warm end packing meansfor the portion ofthe plunger extending through said opening, saidpacking means being spaced at a substantial distance from said pumpingchamber; and a ilow restrictive sleeve in said pump body closely ttingsaid plunger.

14. A reciprocating pump according to claim 13 wherein insulating meanssurrounds a portion of said pump body adjacent the warm end thereof.

15. A reciprocating pump according to claim 13 wherein a heat exchangerpassage surrounds a portion of said pump body adjacent the warm endthereof and is interposed in said discharge valve controlled outletpassage.

16. A reciprocating pump for liquefied gases according to claim 13 inwhich said flow restricting sleeve comprises portions made of alubricant-containing met-al and at least one low thermal conductivityplastic spacer interposed between said portions so as to minimize theflow of frictional heat along the sleeve.

17. A reciprocating pump for liquefied gases according to claim 13 inwhich said flow restricting sleeve comprises portions made of alubricant-containing metal which affords a friction factor between saidplunger and the sleeve of less than about 0.35 said plunger and sleevebeing sized so as to provide a diametrical clearance of about 0.0020 to0.0035 inch at the low operating temperature.

18. A reciprocating pump according to claim 13 wherein said plunger ishollow, constructed of low-conductive material, and sealed at both ends.

19. A reciprocating pump according to claim 18 wherein said pump bodyhas a bore receiving said hollow lowconductive plurrger with a clearanceforming an extended blowby passage in heat exchange with said plungerand a plunger covered vent is provided in the pump body wall adjacentthe warm end thereof.

20. A reciprocating pump according to claim 14 wherein said insulatingmeans comprises a vacuum jacket constructed to maintain a low positivepressure below atmospheric about microns of mercury absolute.

21. A reciprocating pump according to claim 20 wherein said pump body isinstalled in a sump and the diametrical clearance between the vacuumjacket and the inner wall of said sump is sufficiently close in order toprovide a sliding seal between said vacuum jacket and said sump, andincluding sealing means to eiect such seal.

22. A reciprocating pump according to claim 15 wherein said heatexchanger comprises an outer wall, an inner wall having radially outwardprojecting heat transfer tins, and a iiuid space therebetween connectingto said discharge valve controlled outlet passage.

23. A reciprocating pump according to claim 15 wherein said heatexchanger comprises an outer wall, an inner wall having outwardprojecting helically wound heat transfer strips, and a tiuid spacetherebetween connecting to said discharge valve controlled outletpassage.

24. A reciprocating pump for liqueied gases having a boiling point below273 K., said pump comprising an elongated pump body having a pumpingchamber therein adjacent one end and an opening at the other end; aninlet valve controlled port near the end of said pumping chamberopposite said opening; an inlet valve assembly positioned to control owthrough said port having multiple inlet valves protruding into saidpumping chamber such that a space is provided at the lower end of saidpumping chamber not occupied by the valve assembly; a reciprocatingplunger extending through said opening in the pump body having an innerpumping end portion operable in said pumping chamber and constructed andarranged to intert with said multiple inlet valves to substantially illsaid space when at the end of a discharge stroke; a discharge valve anddischarge valve-controlled port near the end of said pumping chamber;warm end packing means for the portion of the plunger extending throughsaid opening, said packing means being spaced at a substantial distancefrom said pumping chamber; and a iiow restrictive sleeve in said pumpbody closely fitting said plunger.

References Cited in the rile of this patent UNITED STATES PATENTS2,292,617 Dana Aug. 11, 1942 2,730,957 Riede Ian. 17, 1956 2,831,325White Apr. 22, 1958 2,888,879 Gaarder .lune 2, 1959

1. A RECIPROCATING PUMP FOR LIQUEFIED GASES HAVING A BOILING POINT BELOW273* K., SAID PUMP COMPRISING AN ELONGATED PUMP BODY HAVING A PUMPINGCHAMBER THEREIN ADJACENT ONE END AND AN OPENING AT THE OTHER END; ANINLET VALVE CONTROLLED PORT NEAR THE END OF SAID PUMPING CHAMBEROPPOSITE SAID OPENING; AN INLET VALVE ASSEMBLY POSITIONED TO CONTROLFLOW THROUGH SAID PORT HAVING AN INLET VALVE PROTRUDING INTO SAIDPUMPING CHAMBER SUCH THAT A SPACE IS PROVIDED AT THE LOWER END OF SAIDPUMPING CHAMBER NOT OCCUPIED BY THE VALVE ASSEMBLY; A RECIPROCATINGPLUNGER EXTENDING THROUGH SAID OPENING IN THE